How to Detect Heat(Estrus) in Pigs: A Breeder’s Guide

Detecting sow heat is one of the most critical tasks for any pig farmer or breeder. Getting the timing right is important because it has a direct impact on conception rates, litter size, and the productivity of the farm.

Understanding the signs of heat and knowing how to accurately check for them can make a big difference in the success of your pig breeding program. With the right knowledge and tools, like the Piggery Manager farm app, farmers can improve breeding outcomes, reduce missed opportunities, and ensure a healthier, more productive herd.

Understanding the Sow’s Estrous Cycle

To manage pig breeding successfully, it’s important to understand how the sow’s reproductive cycle works. The estrous cycle in pigs typically lasts 18 to 24 days, divided into four phases: proestrus, estrus, metestrus, and diestrus. The most important breeding phase is estrus, when the sow is in heat and ready to conceive.

Estrus (heat phase)

This phase usually lasts 36 to 72 hours. The sow is receptive to mating during this time, and ovulation (release of eggs) generally happens 36 to 44 hours after estrus begins. This makes mid-estrus the ideal time for breeding.

After weaning

For sows that have weaned a litter, heat usually returns within 4 to 7 days if the sow is healthy and in good body condition. This is the optimal time to plan for rebreeding.

Gilts (young females)

Gilts reach puberty around 5 to 8 months of age. However, breeding them during their second or third estrous cycle is best to ensure they are physically mature enough for pregnancy.

Recognizing and understanding these phases helps farmers plan breeding at the right time. Since the window of fertility is short, knowing when a sow or gilt is in heat and being prepared to act on time is important for improving conception rates and maintaining a productive herd.

Key Physical Signs of Heat

One of the easiest signs to observe is the condition of the vulva. In sows, the vulva will often become red, swollen, and moist during heat. In gilts, the swelling and color change tend to be even more pronounced.

You may also notice the sow adopting a rigid, upright stance when pressure is applied to her back. This is called the standing reflex or standing heat. A sow or gilt in heat will stay still, indicating she’s ready to be mounted by a boar or prepared for insemination.

Other physical signs include mucus discharge from the vulva and sometimes slight tail flicking. Observing these signs each day helps narrow down the right time for breeding.

Behavioral Changes to Watch For

Behavioral changes are another key indicator. A sow in heat often becomes restless, moving around the pen more than usual. She may display increased vocalization—grunting or squealing—especially when she senses the presence of a boar nearby.

You may also observe her attempting to mount other sows or being more receptive when approached by a boar. Appetite can drop slightly, so a normally eager eater may become less interested in food during heat.

Being familiar with the sow’s usual temperament makes it easier to notice these subtle changes.

The Role of the Boar in Heat Detection

Boars play an important role in helping detect heat in sows and gilts on the farm. Their presence and natural behavior can stimulate and reveal signs of estrus in females, making it easier for farmers to identify the right time for breeding.

When a boar is introduced near or into the pen with sows, his scent, vocalizations, and physical contact help trigger and amplify heat behaviors in the females. These interactions can include sniffing, nudging, grunting, and mounting attempts. The sow’s response to the boar is one of the most reliable indicators of heat.

A sow that is in heat will often:

1. Show increased interest in the boar
2. Allow the boar to sniff and mount her without resistance
3. Stand still when the boar applies pressure, showing the standing reflex
4. Display a swollen and reddened vulva

Boars can help bring sows into heat more consistently and allow the farmer to spot subtle signs that might otherwise be missed when observing the females alone. However, it’s important to use boars carefully and systematically. Bringing the boar to the sows for short periods each day—especially in the morning and evening—can improve heat detection without over-stressing the animals.

For farms using artificial insemination, a teaser boar is often used to identify females in heat. This is a boar that is brought near the sows solely to stimulate and detect estrus, without actual mating.

The boar remains one of the most effective tools for natural heat detection, especially when combined with careful human observation and good record-keeping.

Practical Tips for Effective Heat Detection

Observe twice a day

It’s important to check sows for heat signs twice daily—once early in the morning and again in the evening. These are the cooler times of the day when pigs are more relaxed and easier to observe. Checking at these times increases the chances of spotting subtle behavioral and physical signs of estrus that might be missed when pigs are active or stressed during hotter hours.

Use gentle back pressure

One of the most reliable ways to test if a sow is in heat is to apply gentle pressure on her lower back or rump. A sow in estrus will respond with the standing reflex—she will stand still and remain firm, ready for mating. If she moves away or resists, it usually means she is not yet in heat. This simple hands-on test is a valuable tool for farmers to confirm heat readiness.

Introduce the boar

Bringing a boar near the sow’s pen or allowing short nose-to-nose contact can stimulate the sow and bring out clear heat signs.

The boar’s scent, sounds, and behavior help trigger natural responses in the sow, such as restlessness, mounting behavior, and standing still. This method is especially useful on farms that use artificial insemination and need a reliable way to detect heat without mating.

Keep good records

Writing down details such as the date heat was observed, the signs noticed, and how the sow responded is important for managing breeding effectively. Good records help track each sow’s cycle, predict future heats, and improve breeding success. Over time, this information helps identify patterns, detect problem animals, and plan breeding schedules with greater confidence.

Using tools like the Piggery Manager farm app makes this even easier, allowing you to record, organize, and access all breeding and health data right from your phone, saving time and reducing errors.

Common Mistakes to Avoid When Detecting Heat in Sows.

Successfully detecting heat in sows takes careful observation and good technique. Many farmers struggle not because the sows aren’t showing signs, but because of avoidable mistakes. Here are some of the most common pitfalls to watch out for:

Checking at the wrong time of day

Heat signs are easiest to spot when sows are calm, usually early in the morning or late in the evening. Checking during the heat of the day, when pigs are stressed or distracted, can cause you to miss subtle signs.

Relying on just one sign

Don’t depend on a single heat sign, like a swollen vulva or restlessness. Good heat detection involves looking for a combination of signs, including the standing reflex, vocalization, and mounting behavior, to confirm the sow is truly in estrus.

Skipping the boar exposure

Boar presence is a powerful stimulator of heat signs. Failing to bring the boar near or allowing nose-to-nose contact can reduce the chances of detecting sows in heat, especially in quiet or first-time gilts.

Applying back pressure incorrectly

Pressing too roughly or in a distracting environment can confuse the sow and lead to a false negative on the standing reflex test. Make sure to apply firm but gentle pressure when the sow is calm.

Poor record-keeping

Without accurate records, missing a sow’s heat window or miscalculating when she will return to estrus is easy. Use a notebook or, even better, a tool like the Piggery Manager farm app to track heats, mating dates, and reproductive performance to improve timing and success rates.

Conclusion

Detecting heat in sows is one of the most important skills for achieving breeding success and improving farm productivity. By understanding the sow’s estrous cycle, recognizing physical and behavioral signs, using the boar effectively, and keeping accurate records, farmers can time insemination or mating for the best results.

Avoiding common mistakes and using digital tracking tools can make heat detection more accurate and efficient. With consistent practice and attention, you’ll improve conception rates, increase litter sizes, and strengthen the overall health and performance of your pig herd.